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SpaceShipTwo’s rocket motor test-fired for first time

By Paul Marks

The hybrid rocket motor that is intended to power tourist trips to the edge of space aboard Virgin Galactic’s SpaceShipTwo has undergone its first successful test-firings. The rocket motor’s design incorporates lessons learned after a fatal rocket propellant explosion in 2007.

SpaceShipTwo is designed to be carried to an altitude of 15 kilometres by a carrier plane called WhiteKnightTwo. There, it will detach from the plane and fire its rocket to take passengers to the edge of space, at an altitude of about 100 km.

The pair are scaled-up versions of a carrier plane and spaceship that won the &dollar;10 million Ansari X-Prize for commercial spaceflight in 2004.

Video footage released by Virgin Galactic shows the hybrid motor roaring into life, sending vast plumes of scorched sand into the air.

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“This is a scaled-up version of the SpaceShipOne rocket motor and is, we believe, the largest nitrous oxide hybrid rocket ever built,” says Virgin Galactic’s president, Will Whitehorn.

Its motor is called a hybrid because it burns both liquid oxidiser and solid fuel&colon; volatile nitrous oxide and a benign rubber.

It was during tests with the nitrous oxide that a devastating explosion occurred at Scaled Composites, the California-based company that is building SpaceShipTwo, on 26 July 2007. Three engineers were killed and three more were seriously injured.

Safety features

An enquiry, involving California health and safety officials, industry rocketry experts and NASA, recommended new safety measures (pdf) for the nitrous-fuelled motor, including increasing the compatibility testing between nitrous oxide and any materials that contact it in the tank and diluting nitrous oxide vapour in the tank with an inert gas, such as helium, to decrease its volatility and help pressurise the gas so that it is forced into the rocket.

Whitehorn says the design of Rocket Motor 2, as the new motor is called, has been tweaked with safety in mind&colon; “There are some changes since the first motor was designed, mainly related to additional safety features such as a helium tank.”

The motor will continue to undergo tests and SpaceShipTwo itself is set to begin flight tests later in 2009.

Tests on its carrier jet WhiteKnightTwo are ongoing. A long-range WK2 flight is slated for June, say sources.